The present invention relates to a device and method for testing and calibrating the oscillation frequency of an integrated oscillator.
As is known, many devices formed on silicon currently include digital circuits. Additionally, in the instance of microprocessor and microcontroller chips, a digital part is incorporated in systems of various description, which usually include an analog part as well, to provide an effectual and flexible way of managing different sub-blocks in such systems.
With flash memories, for example, it may be necessary to perform decodings, operate charge pumps and regulators, and drive sense amplifiers and many other elements within the memories themselves, consistently with intended operations.
In such cases, the state of the art proposes implementing a state machine, i.e., a dedicated digital circuit operative to drive control signals within the integrated circuit or chip. In other cases, a microcontroller is incorporated in the chip to perform more complex operations than are allowed by a state machine, which microcontroller may be reconfigured as required.
However, for a digital type of control, a clock signal must be available to the chip which is usually supplied from without the chip, i.e., generated by external elements of the chip, typically quartz-containing elements.
In fact, a major advantage of quartz is that an oscillating signal can be generated at an accurately set frequency.
Thus, many prior solutions have been based on the use of a quartz oscillator circuit formed on a circuit board. Other solutions provide a quartz element connected directly to the chip pins.
In applications such as those affecting flash memories, the digital circuitry portion is arranged to operate essentially within the chip. Accordingly, the end user of the memory device will only be interested in the exchange of data with the memory, and he/she will produce signals relating to the operations in hand.
It is desirable, therefore, that an oscillator circuit be added to generate the clock signal within the chip. In this way, it also becomes possible to keep the number of the external components on the circuit board low, with favorable effects on space requirements and the cost of the finished devices.
However, technological tolerances of the integrated device fabricating process affect the accuracy of the oscillation frequency of an oscillator circuit integrated in a chip.
Embodiments of the present invention include a circuit integrated on a chip that is used in a preliminary chip testing stage to measure an oscillation frequency of a clock signal generated on the chip, and can also be used to calibrate the clock frequency to a particular specification.
The embodiments of the present invention provide a digital autotest device, integrated to a chip, which can measure and calibrate the frequency value of an oscillating signal generated within the chip, upon a signal of known duration being supplied from testing apparatus connected to said chip.
In accordance with one embodiment of the invention, a digital device for testing and calibrating the oscillation frequency of a semi-conductor integrated oscillator is provided. The device includes at least one storage and control section and a plurality of pins connected bi-directionally to the storage and control section, at least one of the input pins receiving a referencing signal of known duration, and having as input at least first and second testing valves. The device further includes a circuit for comparing the signal of known duration and the oscillation frequency signal; a circuit connected to the comparing circuit for generating calibration values from the signal of the integrated oscillator circuit; and a circuit for storing the final calibration values of the signal from the integrated oscillator circuit into the storage and control section.
In accordance with another embodiment of the invention, a testing and calibration system used in conjunction with a semi-conductor integrated oscillator is provided. The system includes a memory, a plurality of pads including first, second, third, and fourth pads; a referential generator adapted to be coupled to the first pad and configured to output a reference signal of known duration; and a testing and calibration circuit having first and second inputs to receive first and second testing values, a first output adapted to be coupled to the second pad for sending testing and calculation control signals, a second output adapted to be coupled to the third pad for sending frequency change signals, and a third input adapted to be coupled to the fourth pad for receiving a results signal.
In accordance with yet another embodiment of the invention, a method for the digital testing and calibration of an oscillation frequency generator in an integrated oscillator circuit is provided. The method includes starting the test and calibration operation; initiating the integrated oscillator circuit; setting a frequency selection signal to a nominal value; setting a counter of clock pulses to a zero starting value; initiating a reference signal of known duration generated by an internal generator; checking the level of the reference signal by means of an internal circuit of a testing and calibration device that is responsive to a change-over edge of the reference signal from a starting value; and incrementing the clock pulse counter and going back to the checking step. Ideally, the method includes after setting a frequency selection to a nominal value, sending first and second control parameters in digital form to the testing and calibrating device.
In accordance with another aspect of the foregoing method, additionally included are verifying that the value of the clock pulse counter lies within the range defined by the control parameters; altering the configuration of the frequency selectors associated with the internal configuration of the frequency selectors associated with the internal oscillator circuit, and going back to the step of setting a counter of clock pulses until the value of the internally generated oscillation frequency are within a predetermined frequency range corresponding to values between a minimum and a maximum; storing the resultant frequency selected values into a permanent storage element as the value of the internally generated oscillation frequency moves into the predetermined frequency range; and ending the test and calibration operation.